The present invention relates to an exhaust gas system with a collector for joining exhaust gas flows from two or more cylinders of a combustion engine. The collector has an outlet cross-section behind which a tubular jacket is connected and a honeycomb body is disposed in the tubular jacket. The invention furthermore relates to a method for applying flows of exhaust gas to a honeycomb body.
Regulations require improvement in the cold starting behavior of combustion engines with respect to their exhaust gas emissions. For that purpose, it is known to provide a first catalytic converter close to the engine, for example closely behind a manifold. Due to the high temperatures behind the manifold, that leads to rapid heating up of the catalytic converter disposed behind it. However, that catalytic converter is also exposed to high degrees of thermal and mechanical shocks at that location, because of pulsating exhaust gas flows.
It is accordingly an object of the invention to provide an exhaust gas system with at least one guide surface and a method for applying exhaust gas flows to a honeycomb body, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and which improve an emission behavior of a combustion engine, in particular in a cold starting phase, and especially improve a useful life of a honeycomb body installed close to an engine.
With the foregoing and other objects in view there is provided, in accordance with the invention, an exhaust gas system, comprising a collector for joining exhaust gas flows from at least two cylinders of a combustion engine. The collector has an outlet cross-section. A tubular jacket is disposed downstream of the outlet cross-section in exhaust gas flow direction. A honeycomb body is disposed in the tubular jacket and defines a space between the outlet cross-section and the honeycomb body for conducting a flow. At least one first guide surface of the tubular jacket is disposed in the space for diverting at least a part of the exhaust gas flows.
Such a first guide surface delays the incidence of the individual exhaust gas flows upon the end surface of the honeycomb body facing the flow. Making the exhaust gas flows turbulent leads to an improved mixing of a total gas flow supplied to the honeycomb body which, in particular, improves the subsequent catalytic reaction. The measurement precision of a lambda probe for measuring oxygen content, which is optionally disposed in the collecting space or to the rear thereof, is increased, since the somewhat uneven composition of the individual exhaust gas flows is at least partially compensated for. As the flows of exhaust gas flow in the form of a pulsating flow into the collector, the first guide surface absorbs a pressure gradient and reduces it. The downstream honeycomb body is relieved to the extent of these pressure gradients. In this way, damage caused by the pulsating flow which could occur over a long period of operation, is advantageously avoided.
It is also advantageous to configure the first guide surface in such a way that the exhaust flows are diverted in front of the honeycomb body. Diversion, which means a substantial change to the original direction of the flow of exhaust gas flows, again delays their incidence upon the honeycomb body, so that in particular, interaction with the next pulse of exhaust gas from another exhaust gas pipe takes place in order to even out the pressure. In particular, a low pressure occurs in an advantageous manner after the pressure pulse, even in the other cylinders. Furthermore, because of the turbulence occurring in this way, it again makes it possible to obtain a good mixing of the fluid flows. A further development of the first guide surface is that it is configured in such a way that the flows of exhaust gas at least partially flow in reverse. This means that the exhaust gas flows are at least partially diverted back in the direction from which they have flowed. The first guide surface is preferably disposed in such a way that it is partly opposite the exhaust gas flows flowing into the chamber. A further development is that the first guide surface is disposed in such a way that direct flowing of the exhaust gas flows onto the honeycomb body is at least partially obstructed.
On one hand, this leads to limiting and preferably completely eliminating linear exposure of the end surface of the honeycomb body. With at least partial obstruction of the flow path, the pressure gradient is at least reduced to the point where possible damage to the honeycomb body occurring over a prolonged period of operation is prevented. Additionally, there are mixing effects between the individual exhaust gas flows. Chemical reactions, as well as homogenization of temperatures, can be obtained through the use of this mixing. Periodic differences in pressure in the individual exhaust gas flows can be compensated for in such a way that after turbulence of the flows has been obtained, a blended total exhaust gas flow impinges upon the end surface of the honeycomb body.
The first guide surface may use a guide plate for this purpose. The guide plate must be capable of absorbing temperature differences and pressure differences which occur. In particular, the first guide surface is configured in such a way that it reduces the free cross-section behind the outlet cross-section, to which in turn the free cross-section of the tubular jacket is joined. The first guide surface is therefore preferably constructed as a type of deflector.
Alternative and/or cumulative configurations of a first guide surface have regular or irregular holes distributed over part or all thereof, and/or notches on a lateral external edge, and/or at least one opening on an edge, and/or at least one arch or curvature on at least one of its surfaces.
An eddy space is preferably provided between the outlet cross section and the first guide surface, as a reaction space. There is sufficient space in the eddy space to ensure, for example, a mixing of the individual exhaust gas flows. Furthermore, this eddy space serves, in a certain way, as a steadying space for the entire exhaust gas flow finally impinging upon the end surface of the honeycomb body. Through the use of suitable dimensioning of the eddy space, the way in which mixing takes place, after eddying caused by the guide surface, can be adjusted. The layout of the eddy space also determines what pressure gradients of the individual exhaust gas flows act against one another, and can finally be homogenized. The eddy space also serves in the formation of an even temperature distribution within the entire exhaust gas flow finally impinging upon the honeycomb body.
Preferably, the first guide surface is disposed closer to the outlet cross-section than to the honeycomb body. For one thing, the guide surface absorbs a pressure gradient much earlier in this way. For another, in this way, a total flow resulting from different coinciding exhaust gas flows behind the guide surface is distributed over the subsequent free cross-section of the tubular jacket in such a way that the entire end surface of the honeycomb body receives the flow, homogenously over its cross-section.
In particular, the formation of rear turbulence behind the guide surface can be avoided, in combination with an appropriate layout of the flow surface. The same applies for the avoidance of areas in which a detached flow and thus an area exists, in which parts of the exhaust gas flow pause for a certain amount of time as compared to the rest of the flow. To the extent that one guide surface is insufficient for obtaining the advantages described, it is proposed to place a second guide surface between the first guide surface and the honeycomb body, in the space through which a flow is to take place.
The collector according to the invention is distinguished in that at least a first guide surface is a component of the collector. If it is, for example, a cast piece, the flow surfaces are cast together with the other parts of the collector in one operation.
The exhaust gas system honeycomb body according to the invention, which is disposed in a tubular jacket, is distinguished in that at least a first guide surface is a component of the tubular jacket. This can, for example, be done by suitable folding or the like during manufacture of the tubular jacket.
Alternative configurations provide that the guide surface for the exhaust gas system is disposed as a replaceable component between the collector and the tubular jacket. It is, for example, to be mounted as an insert in the collector or in the tubular jacket. The guide surface can also be an intermediate flange between the collector and the tubular jacket.
The proposed configuration of at least one guide surface on an edge of the flow path towards the honeycomb body therefore advantageously results in a central cross-section of the space through which a flow is to take place behind the guide surface being kept clear. However, at the same time it offers the inflow of the exhaust gas flows a corresponding opposite surface for producing turbulence.
With the objects of the invention in view, there is also provided a method for applying exhaust gas flows to a honeycomb body, which comprises providing a tubular jacket surrounding the honeycomb body and integrating at least one guide surface in the tubular jacket. The exhaust gas flows are directed at least partly from different directions into a given direction toward the honeycomb body. The exhaust gas flows are diverted with the at least one guide surface at least partly in a direction opposite to the given direction before impinging upon the honeycomb body, thus delaying impingement upon the honeycomb body.
The individual exhaust gas flows are diverted before reaching the honeycomb body in such a way that they flow at least partly in the direction counter to the exhaust gas flow, mix with one another, and only then are incident upon the honeycomb body. This method is particularly preferred when the flows of exhaust gas flow to the honeycomb body in a pressure pulsating manner. The method is also very advantageous when the individual exhaust gas flows flow to the honeycomb body time-offset with respect to one another.
In order to provide further improvement of the emission behavior of a combustion engine, in particular in the cold starting phase, it is proposed that the exhaust gas flows diverted and made turbulent through the use of the first guide surface flow through a second guide surface. In this way, in addition to the advantages described above, in particular the entire end surface of the honeycomb body is advantageously impinged by the flow even more homogenously over its cross-section.
Further advantages and features of the invention will be explained in more detail with reference to the following drawings, which provide additional, advantageous further developments when combined with one another and with the features described hereinabove. The drawings show a preferred area of application of the invention. In addition to the use of the exhaust gas system, the collector, the honeycomb body and the method in an exhaust gas installation of a combustion engine, the invention can also be used in particular where a plurality of individual fluid flows from different directions coincide with one another and directly thereafter impinge upon a honeycomb body with a catalytically active coating. Thus, particular advantages of the invention are obtained for fluid flows which, on one hand, have pressure gradients, are time-offset with respect to one another, in particular flow into one another and react chemically and/or have temperature gradients within the fluid flow or between fluid flows.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an exhaust gas system with at least one guide surface and a method for applying exhaust gas flows to a honeycomb body, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.